1. Field of the Invention
The present invention relates to image data processing techniques and in particular to an image data processing device and method allowing copyright protection.
2. Description of the Prior Art
With wide-spreading digital satellite broadcasting, the Internet, and DVD (Digital Video Disk), etc. in recent years, digital images are becoming easily accessible to users. Since the quality of digital images does not deteriorate when they are copied, copyright protection has been an important issue.
For protection of video contents, motion-picture or still-picture contents, and the like, a scrambling method of scrambling image contents is not so effective. Once its descrambling algorithm has been known by a third person, unauthorized copying cannot be prevented.
As another copyright protection method, there has been proposed a digital watermarking system. More specifically, at a contents provider, watermark data is embedded into DCT (discrete cosine transform) coefficient domain of compressed image data. At a user terminal, it is checked whether a watermark is embedded in the input image data. When the watermark has been detected from the input image data, the watermark detection result is displayed and thereby copying can be effectively prevented (see Japanese Patent Application Unexamined Publication No. 10-155151).
Accordingly, by embedding a watermark indicating that copies of this image data are prohibited, the contents provider can effectively prohibit the user to copy it while playing back. Contrarily, it is possible to embed a watermark indicating that copies of this image data are permitted.
On the other hand, in the music industry, a copy protection system called CGMS (Copy Generation Management System) has been employed to limit to only one copy from a music CD (compact disk) to a MD (minidisk). Copy-once data has been written in the music CD. When the content of the music CD is copied to a MD, the copy-once data is detected and copy-never data is written in the MD. Accordingly, only one copy from the CD to MD is permitted. Such a copy protection system effectively prevents wide-spreading illegal copies.
In a conventional watermarking system, however, a watermark embedded in an image content indicates one of “copy-prohibition” and “copy-free” Accordingly, many contents providers desire to set watermarks embedded in their own contents to “copy-prohibition” so as to avoid copying without limitation. In the case where almost all image contents commercially available are copy-prohibited, however, few consumers will purchase an image recording device having the image copying function, resulting in market reduction.